1. Field of the Invention
The present invention relates to a heat-sensitive recording material, more particularly to a diazo compound-based heat-sensitive recording material which can be fixed and which is excellent in preservability.
2. Description of the Related Art
Heat-sensitive recording materials for recording images by applying heat via a thermal head or the like are widely used since they are relatively cheap, a recording apparatus for use therewith is simple and highly reliable, and maintenance thereof is unnecessary. Under such conditions, there has recently been strong desire for high performance such as high image quality, improved preservation stability and the like, and studies of color developing density, image quality, preservability and other properties of heat-sensitive materials have been intensively conducted.
As heat-sensitive recording materials, those using a diazo compound as a color component for improving color developing density, image quality and preservability have been abundantly developed. In the case of the heat-sensitive recording materials containing diazo compound, an image is formed by heat, then, the diazo compound is thermally decomposed (fixed) with light, and image preservability can be significantly improved by encapsulating the diazo compound.
However, even with the above-mentioned heat-sensitive recording materials containing the diazo compound, a problem is observed in that, after printing an image, a color developed portion thereof becomes discolored over time during storage and image concentration decreases. This has been ascribed to crystallization of an azo dye in the color developed portion with the passage of time. To prevent discoloration of the image resulting from crystallization of this dye, a diazo compound which is not easily crystallized when an azo dye is formed can be effectively used. When the diazo compound which is not easily crystallized is used, however, a problem occurs in that there is a decrease in light resistance of the color developed portion.
An object of the present invention is to solve the above-described problems of the prior art and specifically to provide a heat-sensitive recording material which suppresses discoloration over time without decreasing light resistance of a color developed portion and which has excellent image preservability.
A first aspect of the present invention provides a heat-sensitive recording material comprising a substrate having disposed thereon at least a heat-sensitive recording layer comprising:
microcapsules;
diazonium salt compounds contained within the microcapules and represented by the following general formula (I); and
a coupler which undergoes coupling-reaction with the diazonium salt compounds to cause color development,
wherein three or more of the diazonium salt compounds represented by the general formula (I) are contained in the same microcapsule: 
xe2x80x83(wherein R1, R2 and R3 each independently represents an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group; and Xxe2x88x92 represents a counter anion).
Further, a second aspect of the present invention provides the heat-sensitive recording material of the first aspect at least one of said diazonium salt compounds contained in the microcapsule is a compound represented by the following general formula (II): 
(wherein R1 and R2 each independently represents an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group; R4 represents an alkyl group; and Xxe2x88x92 represents a counter anion).
A heat-sensitive recording material of the present invention will now be described in detail.
The heat-sensitive recording material of the present invention comprises a substrate having disposed thereon at least a heat-sensitive recording layer containing diazonium salt compounds represented by the general formula (I) listed below and a coupler which undergoes coupling reaction with the diazonium salt compound to cause color development, wherein three or more diazonium salt compounds represented by the general formula (I) are contained in the same microcapsule.
In the heat-sensitive recording material of the present invention, crystallization of an azo dye with the passage of time can be suppressed without decreasing light resistance, by allowing three or more diazonium salt compounds represented by the general formula (I) to be contained in the same microcapsule. As a result, discoloration of a color developed portion can be suppressed to improved image preservability. In the heat-sensitive recording material of the present invention, it is necessary that three or more diazonium salt compounds represented by the following general formula (I) are contained in the same microcapsule. Said diazonium salt compounds may be appropriately selected and a number of kinds contained determined so that each diazonium salt compound is contained in an amount of at least 5% by weight. From the standpoint of balancing cost performance and the like with the effect of the invention, however, three or four diazonium salt compounds are preferably contained. 
The heat-sensitive recording material of the invention has at least the heat sensitive recording layer disposed on the substrate, and the heat sensitive recording layer may comprise a single layer or a plurality of layers, and, if necessary, other layers such as a light transmittance controlling layer, a protective layer and the like may further be provided.
Heat-Sensitive Recording Layer
The heat-sensitive recording material of the invention has at least the one heat sensitive recording layer containing microcapsules containing three or more diazonium salt compounds of the above-mentioned general formula (I).
In the above-mentioned general formula (I), R1, R2 and R3 each independently represents an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group. A total number of carbon atoms in R1, R2 and R3 is preferably 12 or more, and more preferably 14 or more.
Examples of the alkyl group include a methyl group, ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a t-butyl group, a pentyl group, an isopentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, an octyl group, a t-octyl group, a 2-ethylhexyl group, a nonyl group, an octadecyl group and the like.
Examples of the substituent of the substituted alkyl group include alkoxy groups, alkoxycarbonyl groups, alkylsulfonyl groups, substituted amino group, substituted amide groups, aryl groups, aryloxy groups, halogen and the like. However, the scope of the invention is not limited thereto. Specific examples of the substituted alkyl group include a benzyl group, 4-methoxybenzyl group, triphenylmethyl group, ethoxycarbonylmethyl group, 2-ethylhexyloxycarbonylmethyl group, methoxyethyl group, ethoxyethyl group, butoxyethyl group, 2xe2x80x2,4xe2x80x2-diisopentylphenyloxymethyl group, 2xe2x80x2,4xe2x80x2-di-t-butylphenyloxymethyl group, dibenzylaminocarbonylmethyl group, 2,4-di-t-aminophenyloxypropyl group, ethoxycarbonylpropyl group, 1-(2xe2x80x2,4xe2x80x2-di-t-aminophenyloxy)propyl group, acetylaminoethyl group, 2-(N,N-dimethylamino)ethyl group, 2-(N,N-dimethylamino)propyl group, methanesulfonylaminopropyl group and the like.
Examples of the substituent of the substituted aryl group include, but are not limited to, alkyl groups, alkoxy groups, alkylthio groups, aryl groups, aryloxy groups, arylthio groups, acyl groups, alkoxycarbonyl groups, carbamoyl groups, carboamide groups, sulfonyl groups, sulfamoyl groups, sulfoneamide groups, ureide groups, amino groups, heterocyclic groups, halogens and the like.
Specific examples of the substituted aryl group include a 2-methylphenyl group, 2-chlorophenyl group, 2-methoxyphenyl group, 2-butoxyphenyl group, 2-(2-ethylhexyloxy)phenyl group, 2-octyloxyphenyl group, 3-(2,4-di-t-pentylphenoxyethoxy)phenyl group, 4-chlorophenyl group, 4-methylphenyl group, 4-methoxyphenyl group, 4-butoxyphenyl group, 2,5-dichlorophenyl group, 2,4,6-trimethylphenyl group, 3-chlorophenyl group, 3-methylphenyl group, 3-methoxyphenyl group, 3-butoxyphenyl group, 3-cyanophenyl group, 3-(2-ethylhexyloxy)phenyl group, 3,4-dichlorophenyl group, 3,5-dichlorophenyl group, 3,4-dimethoxyphenyl group, 3-(dibutylaminocarbonylmethoxy)phenyl group, 4-cyanophenyl group, 4-methylphenyl group, 4-methoxyphenyl group, 4-butoxyphenyl group, 4-(2-ethylhexyloxy)phenyl group, 4-benzylphenyl group, 4-aminosulfonylphenyl group, 4-N,N-dibutylaminosulfonylphenyl group, 4-ethoxycarbonylphenyl group, 4-(2-ethylhexylcarbonyl)phenyl group, 4-fluorophenyl group, 3-acetylphenyl group, 2-acetylaminophenyl group, 4-(4-chlorophenylthio)phenyl group, 4-(4-methylphenyl)thio-2,5-butoxyphenyl group, 4-(N-benzyl-N-methylamino)-2-dodecyloxycarbonylphenyl group and the like.
The alkyl group, the substituted alkyl group, the aryl group and the substituted aryl group may be further substituted, and substituents thereof include alkyl groups, aryl groups, hydroxyl groups, alkyloxy groups, alkylthio groups, arylthio groups, acyl groups, alkoxycarbonyl groups, acyloxy groups, carbamoyl groups, acylamino groups, halogen atoms, cyano group and the like.
Xxe2x88x92 in the general formula (I) represents a counter anion. Examples of the counter anion include polyfluoroalkylcarboxylic acids, polyfluoroalkylsulfonic acids, boron tetrafluoride, tetraphenylboric acids, hexafluorophosphoric acids, aromatic carboxylic acids, and aromatic sulfonic acids, and among these, hexafluorophosphotic acids are preferable.
From the standpoint of sufficient control of crystallization of an azo dye, it is preferable that at least one of the three or more diazonium salt compounds represented by the general formula (I) contained in the same microcapsule is a diazonium salt compound represented by the following general formula (II). 
The diazonium salt compound represented by the general formula (II) is a compound represented by the general formula (I) in which R3 is substituted by an aryl group substituted with an alkyl group, and R1, R2 and Xxe2x88x92 are the same as R1, R2 and Xxe2x88x92 in the general formula (I), and descriptions thereof are therefore omitted. In the general formula (II), R4 represents an alkyl group, and examples of this alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a t-butyl group, a pentyl group, an isopentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, an octyl group, a t-octyl group, a 2-ethylhexyl group, a nonyl group, an octadecyl group and the like. Among these a methyl group and ethyl group are preferable, and a methyl group is particularly preferable.
Specific examples of the diazonium salt compounds represented by the general formulae (I) and (II) are listed below (exemplary compounds (1) to (16)), but the scope of the invention is not limited thereto. 
Among the diazonium salt compounds represented by the general formulae (I) and (II), those having a melting point in a range of from 30xc2x0 C. to 200xc2x0 C. are preferable. When the diazonium salt compounds represented by the general formulae (I) and (II) are contained in microcapsules, they are dissolved in a suitable solvent (for example, tricresyl phosphate, ethyl acetate or the like) before use, and those having suitable solubility in these solvents (for example, 5% by weight or more) are therefore preferable. Each of the diazonium salt compounds represented by the general formulae (I) and (II) preferably has a solubility of 1% by weight or less.
The three or more diazonium salt compounds represented by the general formula (I) used in the invention are used in the heat-sensitive recording layer in a total amount of preferably from 0.02 to 3 g/m2, and, from a standpoint of color developing density, particularly preferably from 0.1 to 2 g/m2. Though a content of each diazonium salt compound, which is based on a total content of all of the diazonium salt compounds, is also determined by the number and properties of the diazonium salt compounds contained in the same microcapsule, if the content of each diazonium salt compound is too small, crystallization suppressing effect may decrease and light resistance may be lowered. Therefore, the content of each diazonium salt compound is preferably at least 5% by weight or more, and further preferably 10% by weight or more. For example, when three of the above-mentioned diazonium salt compounds are used together, it is preferable that each compound is contained in an amount of 15% by weight or more, and further preferably in an amount of 20% by weight or more. When four of the above-mentioned diazonium salt compounds are used together, it is preferable that each compound is contained in an amount of 10% by weight or more, and further preferably in an amount of 15% by weight or more.
When the diazonium salt compound represented by the general formula (II) is used, it is preferable to use in combination therewith a diazonium salt compound represented by the general formula (I) which shows high light resistance when an azo dye is produced. Examples of the diazonium salt compound represented by the general formula (I) which show high light resistance when used to form an azo dye include the above-mentioned exemplary compounds (1), (15) and (16). When the diazonium salt compound represented by the general formula (II) and other diazonium salt compound represented by the general formula (I) are used together, a content of the diazonium salt compound represented by the general formula (II) is preferably from 20 to 50% by weight, and further preferably from 25 to 40% by weight based on a total amount of the three diazonium salt compounds represented by the above-mentioned general formula (I), for compatibility of light resistance of a color developed portion and image preservability.
In the heat-sensitive recording material of the invention, at least one heat sensitive recording layer containing microcapsules containing three or more diazonium salt compounds represented by the general formula (I) may be disposed on a substrate, and additional layers may also be included. The heat-sensitive recording material of the invention may have a laminated construction comprising a heat sensitive recording layer containing a known diazo compound as a color developing component and a coupler, or an electron-donating colorless dye and an electron-accepting compound, and the heat sensitive recording layer of the invention.
Examples of the known diazo compound include diazonium salt compounds represented the following general formula (III):
Arxe2x80x94N2+X1xe2x88x92xe2x80x83xe2x80x83(III) 
(wherein Ar represents a substituted or unsubstituted aryl group, and X1xe2x88x92 represents an acid anion).
The diazonium salt compound represented by the general formula (III) causes a coupling reaction with a later-described coupler by heating, and causes decomposition by light. A maximum absorption wavelength thereof can be controlled by position and kind of a substituent for Ar.
In the general formula (III), Ar represents a substituted or unsubstituted aryl group.
As the aryl group represented by Ar, aryl groups having 6 to 30 carbon atoms are preferable, and examples thereof include a phenyl group, 2-methylphenyl group, 2-chlorophenyl group, 2-methoxyphenyl group, 2-butoxyphenyl group, 2-(2-ethylhexyloxy)phenyl group, 2-octyloxyphenyl group, 3-(2,4-di-t-pentylphenoxyethoxy)phenyl group, 4-chlorophenyl group, 2,5-dichlorophenyl group, 2,4,6-trimethylphenylgroup, 3-chlorophenyl group, 3-methylphenyl group, 3-methoxyphenyl group, 3-butoxyphenyl group, 3-cyanophenyl group, 3-(2-ethylhexyloxy)phenyl group, 3,4-dichlorophenyl group, 3,5-dichlorophenyl group, 3,4-dimethoxyphenyl group, 3-(dibromoaminocarbonylmethoxy)phenyl group, 4-cyanophenyl group, 4-methylphenyl group, 4-methoxyphenyl group, 4-butoxyphenyl group, 4-(2-ethylhexyloxy)phenyl group, 4-benzylphenyl group, 4-aminosulfonylphenyl group, 4-N,N-dibutylaminosulfonylphenyl group, 4-ethoxycarbonylphenyl group, 4-(2-ethylhexylcarbonyl)phenyl group, 4-fluorophenyl group, 3-acetylphenyl group, 2-acetylaminophenyl group, 4-(4-chlorophenylthio)phenyl group, 4-(4-methylphenyl)thio-2,5-butoxyphenyl group, 4-(N-benzyl-N-methylamino)-2-dodecyloxycarbonylphenyl group and the like. These groups may be substituted by an alkyl group, alkoxy group, alkylthio group, aryl group, aryloxy group, arylthio group, acyl group, alkoxycarbonyl group, carbamoyl group, carboamide group, sulfonyl group, sulfamoyl group, alkyloxy group, cyano group, amino group, substituted amino group, halogen atom, heterocyclic group, sulfoneamide group, ureide group, halogen group, heterocyclic group and the like, and these may be further substituted.
Specific examples of the diazonium used to form the diazonium salt represented by the general formula (III) include 4-(p-tolylthio)-2,5-dibutoxybenzenediazonium, 4-(4-chlorophenylthio)-2,5-dibutoxybenzenediazonium, 4-(N,N-dimethylamino)benzenediazonium, 4-(N,N-diethylamino)benzenediazonium, 4-(N,N-dipropylamino)benzenediazonium, 4-(N-methyl-N-benzylamino)benzenediazonium, 4-(N,N-dibenzylamino)benzenediazonium, 4-(N-ethyl-N-hydroxyethyamino)benzenediazonium, 4-(N,N-diethylamino)-3-methoxybenzenediazonium, 4-(N,N-dimethylamino)-2-methoxybenzenediazonium, 4-(N-benzoylamino)-2,5-diethoxybenzenediazonium, 4-morpholino-2,5-dibutoxybenzenediazonium, 4-anilinobenzenediazonium, 4-[N-(4-methoxybenzoyl)amino]-2,5-diethoxybenzendiazonium, 4-pyrrolino-3-ethylbenzenediazonium, 4-[N-(1-methyl-2-(4-methoxyphenoxy)ethyl)-N-hexylamino]-2-hexyloxybenzenediazonium, 4-[N-(2-(4-methoxyphenoxy)ethyl)-N-hexylamino]-2-hexyloxybenzenediazonium, 2-(1-ethylpropyloxy)-4-[di-(di-n-butylaminocarbonylmethyl)amino]benzenediazonium, 2-benzylsulfonyl-4-[N-methyl-N-(2-octanoyloxyethyl)]aminobenzenediazonium and the like.
In the general formula (III), X1xe2x88x92 represents and acid anion, and examples thereof include polyfluoroalkylcarboxylic acids having 1 to 9 carbon atoms, polyfluoroalkylsulfonic acids having 1 to 9 carbon atoms, boron tetrafluoride, tetraphenylboric acid, hexafluorophosphoric acid, aromatic carboxylic acids, aromatic sulfonic acids and the like. Among these, hexafluorophosphoric acids are preferable from a standpoint of crystallinity.
The maximum absorption wavelength xcexmax of the above-mentioned known diazo compound may be appropriately selected depending on conditions of the layer in which it is used and the like, but it is preferably 450 nm or less, and more preferably from 290 to 440 nm. When the maximum absorption wavelength xcexmax exceeds 450 nm, preservability may be reduced, and when it is shorter than the above-mentioned range, image fixing properties and image preservability may decrease and hue may deteriorate depending on a combination with a coupler described below.
It is preferable that the diazonium salt compound of the present invention has 12 or more carbon atoms, has a solubility in water of 1% by weight or less, and a solubility in ethyl acetate of 5% by weight or more.
The diazonium salt compound may be used alone, or two or more may be used in combination depending on specific objectives such as hue control and the like.
As the coupler to undergo a coupling-reaction with the above-mentioned diazonium salt compound to form a dye for color developing, any compounds may be used that can couple with a diazonium salt compound under a basic atmosphere and/or a neutral atmosphere to form a dye, and they can be appropriately selected within a range corresponding to objectivities such as hue control and the like.
Examples of the coupler include resorcinol, phloroglucin, sodium 2,3-hydroxynaphthalene-6-sulfonate, sodium 2-hydroxy-3-naphthalenesulfonate, 2-hydroxy-3-naphthalenesulfonic anilide, 2-hydroxy-3-naphthalenesulfinic morpholinoamide, 2-hydroxy-3-naphthalenesulfonic morpholinopropylamide, 2-hydroxy-3-naphthalenesulfonic-2-ethylhexyloxypropylamide, 2-hydroxy-3-naphthalenesulfonic-2-ethyhexylamide, sodium 1-hydroxy-8-acetylaminonaphthalene-1,6-disulfonate, 1-hydroxy-8-acetylaminonaphthalene-8,6-disulfonic dianilide, 1-hydroxy-2-naphthoic morpholinopropylamide, 1,3-dihydroxynaphthalene, 2,2-dihydroxynaphthalene, 2,3-dihydroxy-6-naphthalenesulfonic anilide, 2-hydroxy-3-naphthoic morpholinopropylamide, 2-hydroxy-3-naphthoic anilide, 2-hydroxy-3-naphthoic-2xe2x80x2-methylanilide, 2-hydroxy-3-naphthoic ethanolamide, 2-hydroxy-3-naphthoic octylamide, 2-hydroxynaphthoic morpholinoethylamide, 2-hydroxynaphthoic piperidinopropylamide, 2-hydroxynaphthoic piperidinoethylamide, 2-hydroxy-3-naphtoic-N-dodecyl-oxy-propylamide, 2-hydroxy-3-naphthoic tetradecylamide, 6-methoxy-2-hydroxy-3-naphthoic anilide, 6-ethoxy-2-hydroxy-3-naphthoic anilide, 6-methoxy-2-hydroxy-3-naphthoic morpholinopropylamide, 6-methoxy-2-hydroxy-3-naphthoic-2-hydroxyethylamide, acetanilide, acetacetanilide, 2-chloro-3-(2,4-di-1-amylphenoxypropylaminocarbonyl)-pivaloylacetanilide, benzoylacetanilide, 1-phenyl-3-methyl-5-pirazolone, 1-(2xe2x80x2,4xe2x80x2,6xe2x80x2-trichlorophenyl)-3-benzamide-5-pyrazolone, 1-(2xe2x80x2,4xe2x80x2,6xe2x80x2-trichlorophenyl)-3-anilino-3-pyrazolone, 1-phenyl-3-phenylacetamide-5-pyrazoline and the like. These couplers may be used alone or in a combination of two or more. A content of the couplers in the heat sensitive recording layer is preferably from 0.1 to 30 parts by weight per 1 part by weight of the diazonium salt compound.
In the heat-sensitive recording material of the invention, a combination of an electron-donating dye precursor and an electron-accepting compound (leuco color developing agent) can also be used, as described above, in addition to a diazo compound and a coupler (diazo color developing agent), as a color developing component. For example, if the heat-sensitive recording material has a plurality of the heat sensitive recording layers on the substrate, at least one layer can contain a leuco color developing agent.
Examples of the electron-donating dye precursor include triarylmethane-based compounds, diphenylmethane-based compounds, thiazine-based compounds, xanthene-based compounds, spiropyrane-based compounds and the like are listed, and among these, triarylmethane-based compounds and xanthene-based compounds are preferable due to high color developing density thereof.
Specific examples thereof include 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (namely, crystal violet lactone), 3,3-bis(p-dimethylamino)phthalide, 3-(p-dimethylaminophenyl)-3-(1,3-dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(2-methylindol-3-yl)phthalide, 3-(o-methyl-p-diethylaminophenyl)-3-(2-methylindol-3-yl)phthalide, 4,40-bis(dimethylamino)benzhydrinbenzyl ether, N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, rhodamine-B-anilinolactam, rhodamine(p-nitroanilino) lactam, rhodamine-B-(p-chloroanilino) lactam, 2-benzylamino-6-diethylaminofluorane, 2-anilino-6-diethylaminofluorane, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-cyclohexylmethylaminofluorane, 2-anilino-3-methyl-6-isoamylethylaminofluorane, 2-(o-chloroanilino)-6-diethylaminofluorane, 2-octylamino-6-diethylaminofluorane, 2-ethoxyethylamino-3-chloro-2-diethylaminofluorane, 2-anilino-3-chloro-6-diethylaminofluorane, benzoyl leuco methylene blue, p-nitrobenzyl leuco methylene blue, 3-methyl-spiro-dinaphthopyrane, 3-ethyl-2-spiro-dinaphthopyrane, 3,3xe2x80x2-dichloro-spiro-dinaphthopyrane, 3-benzylspirodinaphthopyrane, 3-propyl-spiro-dibenzopyrane and the like.
An amount of the electron-donating dye precursor to be included in the heat sensitive recording layer is preferably from 0.1 to 2 g/m2 in light of the same conditions listed previously for the diazonium salt compounds.
Examples of the electron-accepting compound include phenol derivatives, salicylic acid derivatives, hydroxy benzoates and the like, and among these, bisphenols and hydroxy benzoates are preferable.
Specific examples thereof include 2,2-bis(p-hydroxyphenyl)propane (namely, bisphenol A), 4,4xe2x80x2-(p-phenylenediisopropylidene)diphenol (namely, bisphenol P), 2,2-bis(p-hydroxyphenyl)pentane, 2,2-bis(p-hydroxyphenyl)ethane, 2,2-bis(p-hydroxyphenyl)butane, 2,2-bis(4xe2x80x2-hydroxy-3xe2x80x2,5xe2x80x2-dichlorophenyl)propane, 1,1-(p-hydroxyphenyl)cyclohexane, 1,1-(p-hydroxyphenyl)propane, 1,1-(p-hydroxyphenyl)pentane, 1,1-(p-hydroxyphenyl)-2-ethylhexane, 3,5-di(xcex1-methylbenzyl)salicylic acid and polyvalent metal salts, 3,5-di(tert-butyl)salicylic acid and polyvalent metal salts, 3-xcex1,xcex1-dimethylbenzylsalicylic acid and polyvalent metal salts, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, 2-ethylhexyl p-hydroxybenzoate, p-phenylphenol, p-cumylphenol and the like.
A content of the electron-accepting compound in the heat sensitive recording layer is preferably from 0.1 to 30 parts by weight per 1 part by weight of the electron-donating dye precursor.
An organic base is preferably added to the heat sensitive recording layer of the present invention for the purpose of promoting a coupling reaction between the diazonium salt compound and the coupler.
The organic base is preferably contained together with the diazonium salt compound and the coupler in the heat sensitive recording layer, and may be used alone or in a combination of two or more.
Examples of the organic base include nitrogen-containing compounds such as tertiary amines, pyperidines, pyperazines, amidines, formamidines, pyridines, guanidines, morpholines and the like. Further, those described in Examined Japanese Patent Application Publication (JP-B) Nos. 52-46806, 2-24916 and 2-28479 and Japanese Patent Application Laid-Open (JP-A) Nos. 62-70082, 57-169745, 60-94381, 57-123086, 58-1347901, 60-49991, 60-165288 and 57-185430 can also be used.
Among these, particularly preferable examples include piperazines such as N,Nxe2x80x2-bis(3-phenoxy-2-hydroxypropyl)piperazine, N,Nxe2x80x2-bis[3-(p-methylphenoxy)-2-hydroxypropyl]piperazine, N,Nxe2x80x2-bis[3-(p-methoxyphenoxy)-2-hydroxypropyl]piperazine, N,Nxe2x80x2-bis(3-phenylthio-2-hydroxypropyl)piperazine, N,Nxe2x80x2-bis[3-(xcex2-naphthoxy)-2-hydroxypropyl]piperazine, N-3-(xcex2-naphthoxy)-2-hydroxypropyl-Nxe2x80x2-methylpiperazine, 1,4-bis{[3-(N-methylpiperazino)-2-hydroxy]propyloxy}benzene; morpholines such as N-3-(xcex2-naphthoxy)-2-hydroxy]propylmorpholine, 1,4-bis(3-morpholino-2-hydroxy-propyoxy)benzene, 1,3-bis(3-morpholino-2-hydroxy-propyoxy)benzene; piperidines such as N-(3-phenoxy-2-hydroxyproyl)piperidine and N-dodecylpiperidine; and guanidines such as triphenylguanidine, trichlohexylguanidine, and dicyclohexylphenylguanidine.
When the organic base is contained in the heat sensitive recording layer, a content thereof is preferably from 0.1 to 30 parts by weight per 1 part by weight of the diazonium salt compound.
In addition to the above-mentioned organic base, a sensitizer can also be added to the heat sensitive recording layer of the heat-sensitive recording material of the invention for the purpose of promoting a color developing reaction.
The above-mentioned sensitizer is a substance which enhances color developing density in heat recording or decreases a minimum color developing temperature, and which makes the diazonium salt, the organic base, the coupler and the like react more easily by lowering a melting point of the coupler, the organic base, the diazonium salt or the like and by decreasing a softening point of capsule walls.
Specifically, organic compounds of low melting points having within molecules thereof aromatic groups and polar groups in suitable amounts are preferable, and examples thereof include benzyl p-benzyoxybenzoate, xcex1-naphthyl benzyl ether, xcex2-naphthyl benzyl ether, phenyl xcex2-naphthoate, phenyl xcex1-hydroxy-xcex2-naphthoate, xcex2-naphthol-(p-chlorobenzyl) ether, 1,4-butanediol phenyl ether, 1,4-butanediol p-methylphenyl ether, 1,4-butanediol p-ethylphenyl ether, 1,4-butanediol m-mehylphenyl ether, 1-phenoxy-2-(p-tolyloxy)ethane, 1-phenoxy-2-(p-ethylphenoxy)ethane, 1-phenoxy-2-(p-chlorophenoxy)ethane, p-benzylbiphenyl and the like.
As a binder used in the heat sensitive recording layer of the invention, known water-soluble polymer compounds, latexes and the like may be used.
Examples of the water-soluble polymer compound include methylcellulose, carboxylmethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, starch derivatives, casein, gum Arabic, gelatin, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, polyvinyl alcohol, epichlorohydrin-modified polyamide, isobutylene-maleinsalicylic anhydride copolymer, polyacrylic acid, polyacrylic amide and the like, as well as modified substances thereof. Examples of the latexes include styrene-butadiene rubber latex, methyl acrylate-butadiene rubber latex, vinyl acetate emulsion and the like.
In the heat sensitive recording layer of the present invention, it is also preferable to use known antioxidants shown below or the like, for improving durability of a color developed image against light and heat and for reducing yellowing by light of non-printed portions (non-image portions) after being fixed.
Examples of the antioxidants include those described, for example, in European Patent (EP) Nos. 223739, 309401, 309402, 310551, 310552 and 459416, German Patent No. 3435443, JP-A Nos. 54-48535, 62-262047, 63-113536, 63-163351, 2-262654, 2-71262, 3-121449, 5-61166 and 5-119449, and U.S. Pat. Nos. 4,814,262 and 4,980,275.
In the present invention, methods for using components such as the coupler, the organic base, the sensitizer and the like are not particularly restricted, and examples of methods for using such components include solid-dispersion, emulsion-dispersion, polymer-dispersion, latex-dispersion, microcapsulation, and the like.
Method of Producing Microcapsules
In the invention, the three or more diazonium salt compounds represented by the general formula (I) are contained in a microcapsule, for suppressing crystallization of a color developed portion.
As the method of microcapsulating the three or more diazonium salt compounds represented by the general formula (I), conventionally known methods can be used. One example thereof is an interfacial polymerization method in which three or more diazonium salt compounds represented by the general formula (I) are simultaneously dissolved or dispersed in a substantially water-insoluble organic solvent to prepare an oil phase which is mixed with an aqueous phase in which a water-soluble polymer is dissolved. The resulting mixture is emulsion-dispersed by a means such as a homogenizer and then heated to cause a polymer forming reaction at surface of drops of the oil, thereby forming microcapsule walls of a high polymer substance. This interfacial polymerization method can form capsules having uniform particle size in a short period of time and provide a recording material excellent in preservability.
Examples of the above-mentioned organic solvent include, auxiliary solvents of a low boiling point such as acetates, methylene chloride, cyclohexanone and the like, and/or, phosphates, phthalates, acrylates, methacrylates, other carboxylates, fatty amides, alkylated biphenyls, alkylated terphenyls, alkylated naphthalenes, diarylethanes, chlorinated paraffins, alcohol-based solvents, phenol-based solvents, ether-based solvents, monoolefin-based solvents, epoxy-based solvents and the like are listed.
Specific examples thereof include solvents of a higher boiling point such as tricresyl phosphate, trioctyl phosphate, octyldiphenyl phosphate, tricyclohexyl phosphate, dibutyl phthalate, dioctyl phthalate, phthalic dilaurate, dicyclohexyl phthalated, butyl olefinate, diethylene glycol benzoate, dioctyl sevacate, dibutyl sevacate, dioctyl adipate, triocryl trimellitate, acetyltriethyl citrate, octyl maleate, dibutyl maleate, isoamylbiphenyl, chlorinated paraffin, diisopropylnaphthalene, 1,1xe2x80x2-ditolylethane, monoisopropylbiphenyl, diisopropylbiphenyl, 2,4-ditertiary amylphenol, N,N-dibutyl-2-butoxy-5-tertiary octylaniline, 2-ethylhexyl hydroxybenzoate, polyethylene glycol and the like.
Among these, alcohol-based solvents, phosphate-based solvents, carboxylate-based solvents, alkylated biphenyls, alkylated terphenyls, alkylated naphthalenes, and diarylethanes are particularly preferable.
Further, carbonization inhibitors such as hindered phenol, hindered amine and the like may be added to the above-mentioned solvents of a higher boiling point. Among the above-mentioned solvenst of a higher boiling point, those having an unsaturated fatty acid are particularly preferable, and examples thereof include xcex1-methylstyrene dimer and the like. Examples of the xcex1-methylstyrene dimer include MSD100 (trade name, manufactured by Mitsui Toatsu Chemicals Inc.) and the like.
Examples of the water-soluble polymer include polyvinyl alcohol, silanol-modified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, amino-modified polyvinyl alcohol, itaconic acid-modified polyvinyl alcohol, styrene-maleic anhydride copolymer, butadiene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyacrylamide, polystyrenesulfonic acid, polyvinylpyrrolidone, ethylene-acrylic acid copolymer, gelatin and the like, and among these, carboxyl-modified polyvinyl alcohol is preferable.
Emulsions or latexes of hydrophobic polymers and the like can also be used together with the water-soluble polymer. Examples of the emulsion or latex include a styrene-butadiene copolymer, a carboxyl-modified styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer and the like. In this case, conventionally known surfactants and the like may be added as necessary.
As the polymer substance constituting the microcapsule walls, for example, polyurethane resins, polyurea resins, polyamide resins, polyester resins, polycarbonate resins, aminoaldehyde resins, melamine resins, polystyrene resins, styrene-acrylate copolymer resins, styrene-methacylate copolymer resins, gelatin, polyvinyl alcohol and the like are listed. Among these, polyurethane/polyurea resins are particularly preferable.
For example, when polyurethane/polyurea resins are used as a material for the capsule walls, a microcapsule wall precursor such as a polyvalent isocyanate or the like is capsulated and mixed into an oily medium (oil phase) to be used as a core material, a second substance (for example, polyol or polyamine) which reacts with the microcapsule wall precursor to form the capsule walls is mixed into a water-soluble polymer aqueous solution (aqueous phase), and the oil phase is emulsion-dispersed into the aqueous phase. The dispersion is then heated to cause a polymer forming reaction at the surfaces of drops of the oil, and microcapsule walls can thus be formed.
Specific examples of the above-mentioned polyvalent isocyanate compound are listed below, but these are not restrictive examples. Examples thereof include isocyanate prepolymers including diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, diphenylmethane-4,4xe2x80x2-diisocyanate, 3,3xe2x80x2-diphenylmethane-4,4xe2x80x2-diisocyanate, xylene-1,4-diisocyanate, 4,4xe2x80x2-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylenes-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, cyclohexylene-1,4-diisocyanate and the like; triisocyanates such as 4,4xe2x80x2,4xe2x80x3-triphenylmethane triisocyanate, toluene-2,4,6-triisocyanate and the like; tetraisocyanates such as 4,4xe2x80x2-dimethylphenylmethane-2,2xe2x80x2,5,5xe2x80x2-tetraisocyanate and the like; an adduct of hexamethylene diisocyanate and trimethylolpropane; an adduct of 2,4-tolylene diisocyanate and trimethylolpropane; an adduct of xylylene diisocyanate and trimethylolpropane; an adduct of tolylene diisocyanate and hexane triol; and the like.
If necessary, two or more of the above-mentioned compounds may be used together, and among them, those having three of more isocyanate groups in a molecule are particularly preferable.
Also, the above-described method can be used when the above-mentioned diazonium compounds and electron-donating colorless dye and the like are microcapsualted. In the method of microcapsulation, the organic solvents for dissolving other components such as the coupler (and the electron-accepting compound), the organic base, the sensitizer and the like, a microcapsule wall precursor and a second substance reacting therewith, are the same as the above-mentioned organic solvents.
A diameter of the microcapsules is preferably from 0.1 to 2.0 xcexcm, and more preferably from 0.2 to 1.5 xcexcm.
Specific constituent embodiments of multi-color recording materials will be described below.
The heat-sensitive recording material of the invention may be either of a single color heat-sensitive recording material having one heat sensitive recording layer disposed on a substrate, and a multi-color heat-sensitive recording material having a heat sensitive recording layer of laminated structure comprising a plurality of single color recording layers.
Particularly in the case of a full color heat sensitive recording layer containing cyan, yellow and magenta, a heat-sensitive recording material in which a substrate is disposed with three layers all comprising diazo color developing agents, or in which a first heat-sensitive recording layer adjacent to the substrate comprises a leuco color developing agent containing an electron-donating dye and an electron-accepting compound and second and third layers comprise diazo color developing agents is preferable. The heat-sensitive recording material of the present invention preferably has a construction in which the substrate is laminated with heat-sensitive recording layers respectively developing colors of cyan, magenta and yellow in this order. In particular, it is optimum that the heat sensitive recording layer of the present invention including microcapsules containing three or more diazonium salt compounds represented by the general formula (I), is the heat-sensitive recording layer developing yellow.
The heat-sensitive recording material of the invention may also be constructed according to the following embodiments (a) to (c).
Embodiment (a) provides a recording material laminated with a light fixation recording layer (first recording layer (layer A)) containing diazonium salt compounds having maximum absorption wavelength of 365xc2x140 nm and a coupler which reacts with the diazonium salt compounds to perform color developing, and a light fixation recording layer (second recording layer (layer B)) containing diazonium salt compounds having maximum absorption wavelength of 420xc2x140 nm and a coupler which reacts with the diazonium salt compounds to develop color, and, if necessary, further laminated with a light transmittance controlling layer and protective layer.
Embodiment (b) provides a recording material comprising a substrate laminated in the following order to a recording layer (first recording layer (layer A)) containing an electron-donating dye and an electron-accepting compound, a light fixation recording layer (second recording layer (layer B)) containing diazonium salt compounds having maximum absorption wavelength of 365xc2x140 nm and a coupler which reacts with this diazonium salt compounds to perform color developing, and a light fixation recording layer (third recording layer (layer C)) containing diazonium salt compounds having maximum absorption wavelength of 420xc2x140 nm and a coupler which reacts with the diazonium salt compounds to perform color developing, and, if necessary, further laminated with a light transmittance controlling layer and protective layer.
Embodiment (c) provides a recording material comprising a substrate laminated in the following order with a light fixation recording layer (first recording layer (layer A)) containing diazonium salt compounds having maximum absorption wavelength of 350 nm or less and a coupler reacting with the diazonium salt compounds to perform color developing, a light fixation recording layer (second recording layer (layer B)) containing diazonium salt compounds having maximum absorption wavelength of 365xc2x140 nm and a coupler which reacts with the diazonium salt compounds to perform color developing, and a light fixation recording layer (third recording layer (layer C)) containing diazonium salt compounds having maximum absorption wavelength of 420xc2x140 nm and a coupler which reacts with the diazonium salt compounds to perform color developing, and, if necessary, further laminated with a light transmittance controlling layer and protective layer.
A method of multi-color recording is described below using the recording material of the embodiments (b) or (c).
First, the third recording layer (layer C) is heated, to allow a diazonium salt and a coupler contained in this layer to color develop. Next, an unreacted diazonium salt compound contained in the layer C is irradiated with light having an emission center wavelength of 430xc2x130 nm so as to be decomposed and cause light fixation. Then, sufficient heat is applied for color development of the second recording layer (layer B), or specifically to cause color development of a diazonium salt compound and a coupler contained in this layer. In this procedure, the layer C is also strongly heated but since the diazonium salt compounds contained therein has already decomposed (light fixed) and thereby lost color developability, color development does not occur. Further, a diazonium salt compound contained in the layer B is irradiated with light having an emission center wavelength of 360xc2x120 nm so as to be decomposed and cause light fixation. Then, finally, heat sufficient for color development of the first recording layer (layer A) is applied to cause color development. In this procedure, the layer C and the layer B are also simultaneously strongly heated, however, since the diazonium salt compounds contained therein have already decomposed to lose color developability, color development does not occur.
When all of the recording layers (layer A, layer B and layer C) are diazo-based recording layers, it is necessary that the layer A and the layer B are subjected to light fixation after color development. The layer C, however, which is image-recorded last, is not necessarily required to be light-fixed.
A light source used for light fixation can be appropriately selected from known light sources, and examples thereof include various fluorescent lamps, xenon lamps, mercury lamps and the like. Among these, light sources having an emission spectrum approximately coinciding with the absorption spectrum of the diazonium salt compounds used in the recording material are preferable for high-efficiency light fixation.
In the heat-sensitive recording material of the present invention, embodiments having a light transmittance controlling layer and a protective layer further disposed on the substrate in addition to the single or the plurality of heat-sensitive recording layers are preferable.
Light Transmittance Controlling Layer
The light transmittance controlling layer contains an ultraviolet absorber precursor. This precursor does not function as an ultraviolet absorber, and the layer has high transmittance before irradiation with light having a wavelength in a range necessary for fixation. Therefore, when the light fixation heat-sensitive recording layer is fixed, light of a wavelength within the range necessary for fixation is sufficiently transmitted. Further, transmittance of visible light is also high, and consequently, fixation of the heat sensitive recording layer is not disturbed. It is preferable that this ultraviolet absorber precursor is contained in microcapsules.
Examples of the compounds contained in the light transmittance controlling layer include those described in JP-A No. 9-1928.
After completion of irradiation with light having a wavelength in a range necessary for fixation of the heat sensitive recording layer, a reaction is caused with the aid of light, heat or the like, whereby the ultraviolet absorber precursor subsequently functions as an ultraviolet absorber, and most light in the ultraviolet region having wavelengths within the range necessary for fixation is absorbed by the ultraviolet absorber, and transmittance lowered and light resistance of the heat-sensitive recording material is improved. The light transmittance controlling layer does not absorb visible light, however, and transmittance of visible light does not substantially change.
At least one light transmittance controlling layer can be provided in the heat-sensitive recording material, and most preferably be formed between the heat-sensitive recording layer and an outermost protective layer. The light transmittance controlling layer, however, may also function the protective layer simultaneously. The properties of the light transmittance controlling layer can be appropriately selected depending on the properties of the heat sensitive recording layer.
An application solution for forming the light transmittance controlling layer (light transmittance controlling layer application solution) is obtained by mixing the above-mentioned components. This light transmittance controlling layer application solution can be applied by a known application means such as a bar coater, an air knife coater, a blade coated, a curtain coater and the like to form the light transmittance controlling layer. The light transmittance controlling layer may be applied simultaneously with the heat sensitive recording layer and the like. Alternatively, for example, the solution may be applied to the recording layer to form the light transmittance controlling layer after an application solution for forming the heat-sensitive recording layer is applied and dried.
A dry application amount of the light transmittance controlling layer is preferably from 0.8 to 4.0 g/m2.
Protective Layer
The protective layer contains a pigment, lubricant, a surfactant, a dispersing agent, a fluorescent whitening agent, a metal soap, a film hardener, an ultraviolet absorber, a cross-linking agent and the like, together with a binder.
The binder can be appropriately selected from among polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, starches, gelatins, gum Arabic, casein, styrene-maleic anhydride copolymer hydrolyzate, ethylene-maleic anhydride copolymer hydrolyzate, isobutylene-maleic anhydride copolymer hydrolyzate, polyvinyl alcohol, denatured polyvinyl alcohol, polyacrylamide and the like, and used in an amount not deteriorating barrier property and workability.
Additional examples of the binders include synthetic rubber latex, synthetic resin emulsion and the like, and examples thereof include styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, vinyl acetate emulsion and the like.
A content of the above-mentioned binder is preferably from 10 to 500% by weight, and more preferably from 50 to 400% by weight based on the pigment contained in the protective layer.
In order to further improve water resistance, it is effective to use a cross-linking agent together with a catalyst for promoting a reaction. Examples of the cross-linking agent include epoxy compounds, blocked isocyanates, vinylsulfone compounds, aldehyde compounds, methylol compounds, boric acid, carboxylic anhydrides, silane compounds, chelate compounds, halides and the like, and those which can adjust the pH level of an application solution for forming a protective layer to within a range of 6.0 to 7.5 are preferable. Examples of the catalyst include known acids, metal salts and the like, and those which can adjust the pH level of the application solution to within a range of 6.0 to 7.5 are preferable as described above.
Known organic or inorganic pigments can be used as the pigment, and specific examples thereof include calcium carbonate, aluminum hydroxide, barium sulfate, titanium oxide, talc, agalmatolite, kaolin, calcinated kaolin, amorphous silica, colloidal silica, urea formalin resin powder, polyethylene resin powder, benzoguanamine resin powder and the like. These can be used alone or as a mixture of two or more thereof.
Suitable examples of the lubricant include zinc stearate, calcium stearate, paraffin wax, polyethylene wax and the like.
Alkali metal salts of sulfosuccinic acid type, fluorine-containing surfactants and the like are suitably used as the surfactant so that the protective layer can be uniformly formed on the heat sensitive recording layer. Specific examples thereof include sodium salts and ammonium salts of di-(2-ethylhexyl)sulfosuccinic acid, di-(n-hexyl)sulfosuccinic acid, and the like.
The application solution for forming a protective layer (protective layer application solution) is obtained by mixing the above-mentioned components. Further, if necessary, a releasing agent, wax, water-repelling agent and the like may be added.
The heat-sensitive recording material of the present invention can be formed by applying the protective layer application solution to the heat-sensitive recording layer formed on the substrate, by a known application method, and examples thereof include methods using a bar coater, an air knife coater, a blade coater, a curtain coater or the like.
The protective layer may be applied together with the heat-sensitive recording layer and the light transmittance controlling layer. Alternatively, the protective layer is applied and formed on the recording layer after the application solution for forming the heat-sensitive recording material is applied and dried.
A dry application amount of the protective layer is preferably from 0.2 to 7 g/m2, and more preferably from 1 to 4 g/m2. When the dry application amount is less than 0.2 g/m2 , water resistance may not be maintained, and when greater than 7 g/m2, heat sensitivity may remarkably decrease. After application and formation of the protective layer, calender treatment may be performed, if necessary.
Intermediate Layer
When the substrate is laminated with a plurality of the heat-sensitive recording layers, it is preferable to provide an intermediate layer between heat-sensitive recording layers. In the intermediate layer, a pigment, a lubricant, a surfactant, a dispersing agent, a fluorescent whitening agent, a metal soap, an ultraviolet absorber and the like can be contained in various binders, as in the protective layer. As the binder, the same binders as those listed for the protective layer can be used.
Substrate
For the substrate, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), triacetylcellulose (TAC), paper, plastic resin laminated paper, synthetic paper and the like can be used. Further, for obtaining a transparent heat-sensitive recording material, it is necessary to use a transparent substrate, and synthetic polymer films including polyester films such as polyethylene terephthalate, polybutylene terephthalate and the like, cellulose triacetate films, polyolefin films such as polypropylene, polyethylene and the like, are examples thereof.
The substrate can be used alone or in laminated form.
The thickness of the above-mentioned synthetic polymer film is preferably from 25 to 300 xcexcm, and more preferably from 100 to 250 xcexcm.
The synthetic polymer film may be colored any hue, and as a method for coloring the polymer film, a dye can be kneaded into a resin prior to film formation. In another method, a dye is dissolved in a suitable solvent which is applied to a transparent colorless resin film by a known application method, such as a gravure coat method, a roller coat method, a wire coat method or the like, and then dried. Other methods may be used as well. Particularly preferably, a polyester resin such as polyethylene terephthalate, polyethylene naphthalate or the like, with a blue dye kneaded therein is molded into a film, and heat-resistance treatment, drawing treatment, antistatic treatment are performed thereon.
The heat-sensitive recording layer, the protective layer, the light transmittance controlling layer, the intermediate layer and the like can be formed by applying respective solutions to the substrate by a known application method, such as a blade application method, an air knife application method, a gravure application method, a roll coating application method, a spray application method, a dip application method, a bar application method and the like, and then drying.